In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, a hot process gas is generated, such process gas containing, among other components, sulfur oxides, such as sulfur dioxide, SO2, and carbon dioxide CO2. With increasing environmental demands various processes for removing carbon dioxide from the process gas have been developed. One such process is the so called oxy-fuel process. In an oxy-fuel process a fuel, such as those fuels mentioned above, is combusted in the presence of a nitrogen-lean gas. Oxygen gas, which is provided by an oxygen source, is supplied to a boiler in which the oxygen gas oxidizes the fuel. In the oxy-fuel combustion process a carbon dioxide rich flue gas is produced, the carbon dioxide content of which can be compressed in a separate unit and be disposed of in order to reduce the emission of carbon dioxide into the atmosphere.
An example of an oxy-fuel boiler is described in US 2007/0243119. The oxy-fuel boiler of US 2007/0243119 generates a process gas which is referred to as a flue gas. The flue gas is directed to a particulate collector for removing dust particles from the flue gas. Then the flue gas is forwarded to a spray tower unit in which sulfur dioxide is removed by means of being brought into contact with a lime stone slurry. The spray tower unit also provides a cooling of the flue gas to condense a portion of the water content of the flue gas.